Tooth positioners are well known orthodontic appliances formed as an arch shaped body of resilient material fitting within a patient's mouth between the upper and lower arches. Tooth positioners have a generally concave surface for bearing on the buccal and labial surfaces of the teeth of at least one arch and a convex surface adjacent to the lingual surface of the patient's teeth. Tooth positioners for moving teeth into a more desired configuration are made by taking a cast of the upper and lower arches, moving teeth in the cast counterpart to more preferred positions, packing or pouring uncured material around the counterpart, curing this material to form a resilient arch shaped body, and trimming the outer surfaces of the body as necessary to make a finished appliance. Such tooth positioners are described, for example, in U.S. Pat. Nos. 2,467,432 and 2,531,222.
Such tooth positioners can be difficult to secure in the proper position in the patient's mouth, particularly when the tooth impressions in the positioner have been moved with respect to the existing positions of the patient's teeth. Deformation of such an appliance to fit it in the patient's mouth frequently creates stresses which tend to unseat or displace part of the tooth positioner from its proper position, thus limiting its therapeutic value. In prior art tooth positioners this seating problem has been addressed by providing protruding metal clips or hooks in the positioner to engage the patient's teeth. If properly anchored, such clips or hooks can assist in seating the positioner, but concentrate the force in very small areas. In some patients they may damage teeth or cause pain when the positioner is worn particularly if they terminate at or near the gum line. In another approach, taught in U.S. Pat. No. 4,055,895 (issued to Huge to Nov. 1, 1977), prestressed elastic bands are incorporated in the tooth positioner so that inward pressure, which can assist in seating the tooth positioner, is exerted on all the teeth of one or both arches. But in certain circumstances prestressed bands in the tooth positioner do not completely solve the seating problem.
Such tooth positioners also must have minimal bulk and weight, especially in the bite portions, to provide a correct and comfortable--or "anatomical"--fit. Yet, the positioners must be durable to resist bite-through and must have sufficient tensile strength and elasticity to move the patient's teeth to the desired positions. Previous positioners have not reached these goals, or have reached one at the expense of another.
Finally, tooth positioners have been made having two or more integrally formed portions of different hardness; one example of such a device is a tooth positioner made with relatively soft tooth engaging portions and a hard shell-like front to stiffen the appliance and to enable it to protect the patient's teeth while the device is worn. The harder part of the appliance does not engage the patient's teeth to assist in anchoring it in place.